1. Field of the Invention
The present invention relates generally to spray guns for applying a stream of paint under pressure. More specifically, the present invention relates to a controlled fan spray gun with a high volume paint output and a low total air pressure in the air cap, or discharge end, of the spray gun.
2. Description of the Related Art
In conventional paint spray guns, a stream of paint under pressure is discharged from a relatively small orifice in a nozzle while air under pressure is discharged radially inwardly into the stream from an annular opening surrounding the nozzle closely adjacent the paint discharge orifice to atomize the stream of paint into a spray of fine particles. The spray thus produced moves away from the gun in an expanding or conical pattern whose apex is at the nozzle.
It is frequently desired to modify, or control, the circular cross-section, or fan, of the normally conical spray pattern by transforming this pattern into one of a narrowed and elongated, generally elliptically shaped cross-section, so that the spray pattern is that of a flat sided fan. This is done by diverting pressurized air within the air cap of the gun laterally into the conical spray emerging from the nozzle, as is well known in the art.
Heretofore such spray guns were largely run on pressurized air lines or tanks at air pressures which caused a large percentage of the paint to bounce back from the surface being painted. This "bounce-back" of paint and the solvents therein wastes paint, or other sprayed coating materials, and pollutes the atmosphere.
In order to decrease this pollution, governmental agencies have enacted regulations to limit the total air pressure available to atomize and propel paint at the discharge end of the spray gun or air cap.
In spite of these regulations, due to inherent design constraints, the delivery systems for pressurized air generally run at pressures higher than the maximum allowable pressure, e.g., 10 psi maximum total air cap pressure is currently required under California law. Thus, the air flowing into the spray gun must be regulated before reaching the air cap.
It is known in the art to have a variable position restrictor plug placed in the air intake passages as disclosed in U.S. Pat. No. 4,187,872. However, this patent discloses no fixed air metering air cap pressure unlike the present invention.
In applicant's prior U.S. Pat. No. 4,744,518, to control the fan of the output spray, there is taught a sliding valve means between the atomizing air and fanning air channels, the disclosure of which is hereby incorporated by reference.
Another known method for regulating air pressure to a spray gun air cap is provided in a single-metering spray gun manufactured by Binks Manufacturing Co. The Binks spray gun places a pierced air restrictor collar, or baffle, and a control rod within an air intake channel. The control rod regulates the flow between a fanning air chamber and an atomizing air chamber formed in the air cap by adjustably locating a tapered end thereof at the intake of the chambers. The restrictor collar, which is a plastic disc provided with restriction orifices, allows only a predetermined air pressure to proceed through the air intake channel to the cap. The Binks single-metering system is designed as a part of a unitary spray gun assembly. This system necessarily requires replacement of the user's current spray gun with a new gun.
It becomes apparent that what is needed in response to lowered air cap pressure regulations in the spray gun art is a device which allows owners of spray guns, currently unable to meet air cap pressure standards, to retrofit their existing guns with an assembly which permits meeting the air pressure standards, while maintaining the operational capabilities of state of the art spray guns as to fan control, paint volume etc. Such a retrofit device should further provide components with design flexibility in meeting the standards, preferably with the minimal amount of machining necessary for such components, i.e., a simplicity of design to yield manufacturing savings in tooling, man hours, and material. By the same token, such a "retrofit" assembly can be employed as part of a new gun. It is to this to which the present invention is directed.